Example: A connectionless client
This example shows how to use User Datagram Protocol (UDP) to connect a connectionless socket client program to a server.
Note: By using the examples, you agree to the terms of the Code license and disclaimer information.
/**************************************************************************/
/* This sample program provides a code for a connectionless client. */
/**************************************************************************/
/**************************************************************************/
/* Header files needed for this sample program */
/**************************************************************************/
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
/**************************************************************************/
/* Constants used by this program */
/**************************************************************************/
#define SERVER_PORT 3555
#define BUFFER_LENGTH 100
#define FALSE 0
#define SERVER_NAME "ServerHostName"
/* Pass in 1 parameter which is either the */
/* address or host name of the server, or */
/* set the server name in the #define */
/* SERVER_NAME */
void main(int argc, char *argv[])
{
/***********************************************************************/
/* Variable and structure definitions. */
/***********************************************************************/
int sd, rc;
char server[NETDB_MAX_HOST_NAME_LENGTH];
char buffer[BUFFER_LENGTH];
struct sockaddr_in6 serveraddr;
int serveraddrlen = sizeof(serveraddr);
struct addrinfo hints, *res;
/***********************************************************************/
/* A do/while(FALSE) loop is used to make error cleanup easier. The */
/* close() of the socket descriptor is only done once at the very end */
/* of the program. */
/***********************************************************************/
do
{
/********************************************************************/
/* The socket() function returns a socket descriptor, representing */
/* an endpoint. The statement also identifies that the INET6 */
/* (Internet Protocol) address family with the UDP transport */
/* (SOCK_DGRAM) will be used for this socket. */
/********************************************************************/
sd = socket(AF_INET6, SOCK_DGRAM, 0);
if (sd < 0)
{
perror("socket() failed");
break;
}
/********************************************************************/
/* If an argument was passed in, use this as the server, otherwise */
/* use the #define that is located at the top of this program. */
/********************************************************************/
if (argc > 1)
strcpy(server, argv[1]);
else
strcpy(server, SERVER_NAME);
memset(&serveraddr, 0, sizeof(serveraddr));
serveraddr.sin6_family = AF_INET6;
serveraddr.sin6_port = htons(SERVER_PORT);
rc = inet_pton(AF_INET6, server, &serveraddr.sin6_addr.s6_addr);
if (rc != 1)
{
/*****************************************************************/
/* The server string that was passed into the inet_pton() */
/* function was not a hexidecimal colon IP address. It must */
/* therefore be the hostname of the server. Use the */
/* getaddrinfo() function to retrieve the IP address of the */
/* server. */
/*****************************************************************/
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_INET6;
hints.ai_flags = AI_V4MAPPED;
rc = getaddrinfo(server, NULL, &hints, &res);
if (rc != 0)
{
printf("Host not found! (%s)", server);
break;
}
memcpy(&serveraddr.sin6_addr,
(&((struct sockaddr_in6 *)(res->ai_addr))->sin6_addr),
sizeof(serveraddr.sin6_addr));
freeaddrinfo(res);
}
/********************************************************************/
/* Initialize the data block that is going to be sent to the server */
/********************************************************************/
memset(buffer, 0, sizeof(buffer));
strcpy(buffer, "A CLIENT REQUEST");
/********************************************************************/
/* Use the sendto() function to send the data to the server. */
/********************************************************************/
rc = sendto(sd, buffer, sizeof(buffer), 0,
(struct sockaddr *)&serveraddr,
sizeof(serveraddr));
if (rc < 0)
{
perror("sendto() failed");
break;
}
/********************************************************************/
/* Use the recvfrom() function to receive the data back from the */
/* server. */
/********************************************************************/
rc = recvfrom(sd, buffer, sizeof(buffer), 0,
(struct sockaddr *)&serveraddr,
& serveraddrlen);
if (rc < 0)
{
perror("recvfrom() failed");
break;
}
printf("client received the following: <%s>\n", buffer);
inet_ntop(AF_INET6, &serveraddr.sin6_addr.s6_addr,
buffer, sizeof(buffer));
printf("from port %d, from address %s\n",
ntohs(serveraddr_sin6_port), buffer);
/********************************************************************/
/* Program complete */
/********************************************************************/
} while (FALSE);
/***********************************************************************/
/* Close down any open socket descriptors */
/***********************************************************************/
if (sd != -1)
close(sd);
}